A battery module including a battery cell and a thermal management system for removing heat from the battery cell. The thermal management system includes two or more unit cells in an array. Each unit cell includes a primary shell comprising a primary phase change material (PCM), and a secondary shell comprising a secondary PCM that is thermally coupled to the primary shell. The battery cell is thermally coupled to the primary shell at a heat transfer interface and the secondary shells of adjacent unit cells in the array are separate.